This and a companion project (Z01 HD001123) investigate auditory communication in primates. The overall goal of these studies is to provide a comprehensive understanding of primate auditory communication in terms of development, neural mechanisms, endocrine factors, and social context. Two species, the squirrel monkey and the common marmoset, are the main subjects of study, with additional data collected from other species where appropriate. The present project studies primate communication from a bioacoustic and ethological perspective, focusing on the detailed acoustic structure of vocalizations produced in natural settings, and the relationship of structural differences to differences in age, gender, experience and response selectivity, as well as the broader factors of social context and genetic background. New findings this year: In a new initiative begun last year to determine the genetic factors underlying expression of a range of behaviors in the common marmoset, infant cries have been analyzed in detail to identify acoustic markers that are shared by sibs, family members or other genetically related individuals. A Summer IRTA Fellow, Karen Ladd, used ?Raven? (a software program developed at Cornell University?s Bioacoustics Program) to measure specific points on sonagraphic displays of infant cries, then wrote a macro in Microsoft Excel that calculated more than 20 parameters from these measures. A total of 3162 cries from 2 and 3-month old infants as well as calls from adult marmosets were measured. A high degree of individuality came out of the analysis, supporting earlier findings. In addition, and of great interest, was the finding that sibs (fraternal twins) shared sufficient acoustic characteristics so that sib pairs were accurately classified and found distinct using discriminant function analysis. Other findings: sex differences in cry structure emerge as early as 2 months of age; syntax in cry structure (the structure and relationship of a pair of syllables making up a cry bout) could be demonstrated at 2 months. These findings suggest a tight regulation of marmoset cry structure starting early in infancy, raising the probably that cry structure is under tight genetic control. A second project is aimed at understanding the significance of crying, and the role of cry acoustics, in caregiver responses to vocalizing infants. A paradigm was developed using a playback technique and Y-maze, in which adult and juvenile marmosets were individually tested for their response (phonotaxic orientation) to crying infants or a loud speaker presenting a digitized cry bout. Of 8 adults with parenting experience, 7 gave positive reponses to live infants on at least 1 of 2 trials. Of seven older offspring (brothers and sisters of the stimulus infants), all failed to give a positive response (4 failing to leave the starting position in the maze). In a second series of trials run 6 months later with the same subjects (after new infants were born to 1 pair in the colony), the actual parents gave positive responses but no other subject responded positively. A variation of this paradigm used cries presented through a loud speaker instead of a live infant. In testing when live infants were present in the colony room, 5 of 7 adults with parenting experience approached the speaker presenting cry sounds.